1. Field of the Invention
The invention relates generally to the field of interventional optical catheters and, more specifically, to a flexible terminus or tip for transluminal surgical catheters and the like.
2. Prior Art
The use of energy delivered from a light source, for example, a laser, for surgical and industrial applications is well documented. Typically, optical waveguides such as silica optical fibers (alternatively referred to herein as "fiber optics") are used to deliver light energy to internal areas of the human body not readily accessed directly by the light source. A growing number of procedures, such as laparoscopic cholecystectomy, laparoscopic appendectomy, lithotripsy of calculi of the biliary, salivary and urinary tracts, and a host of other light energy surgeries require flexible fiber optics to access and deliver substantial energy to the treatment sight.
Often, fiber optics which are flexible enough to access deep, tortuous internal areas of the body are so small in diameter that they lack the rigidity required to push them through the lumen and/or excessive energy density in the fiber causes damage to the fiber rendering such thin fiber optics impractical. Moreover, transmitting higher powers, on the order of 10 or more watts, is inefficient in small fibers due to the difficulty of coupling. Energy density at the fiber optic tip is the total energy delivered divided by the cross sectional area of the optical fiber.
High energy densities cause undesired damage to the tip of the fiber. The solution to this problem, with present technology, is either using larger core diameter optical fibers, which while reducing the energy density, substantially reduces the flexibility (doubling the core size reduces the flexibility fourfold), or using a bundle of small core diameter fiber optics creating a large proportion of dead space. Dead space, as used herein, refers to the portion of the cross sectional area of a fiber optic catheter which does not transmit light energy.
Large core fiber optics permit the relatively efficient coupling of energy from an external source into the fiber; even if the source is divergent. This is not true of small core fibers. The coupling efficiency of large cores together with their rigidity enables them to be readily advanced through a straight lumen and conduct a large amount of light energy to the tip. The disadvantage is that the tip lacks the flexibility to follow a tortuous path.
With conventional laser catheter tips heat buildup is a significant problem. Sapphire or another expensive heat-stable material is frequently used at the tip of such catheters to prevent heat-induced fracturing and subsequent disintegration. Laser surgery is conveniently done by using a flexible quartz fiber for transmitting the laser energy, usually from a Nd:YAG laser source, to the tissue undergoing treatment. In a typical laser surgery system the end or tip of the silica fiber optic serves as the probe for radiating the tissue to effect incision or coagulation thereof. With some fiber optic tips it is desirable to hold the tip away from direct contact with the tissue to avoid fouling of the fiber and, importantly, to avoid heat damage to the fiber end. Noncontact laser systems employing a light transmitting member at the output end of the fiber to focus or otherwise alter the radiation characteristics of the fiber have also been proposed, for example, by Enderly in U.S. Pat. No. 4,273,109, and by Daikuzono in U.S. Pat. No. 4,736,743. Microlenses may also be employed to distribute the light exiting the catheter. The problem with the foregoing termini for laser catheters is that they lack the flexibility to enter small tortuous tubular members such as blood vessels, vas deferens, ureters and so forth.